1. Field of the Invention
The present invention relates to a recording medium in which optically detectable pits and magneto-optically detectable grooves are arranged so as to form a sequential spiral-shaped track and a recording medium master used for manufacturing the recording medium, and to a method of manufacturing the same.
2. Description of the Related Art
An optical recording medium records or reproduces (reads-out) information or data based on the reflection light of the laser irradiated with respect to a signal recording layer of a substrate in a data recording/reproducing apparatus. Examples of known optical recording media are optical discs such as a CD-ROM (Compact Disc-Read Only Memory), and a magneto-optical disc or a phase-change optical disc capable of rewriting signals.
In general, for example, formed on a recording medium such as MD (Mini Disc) are grooves for recording various kinds of information as recording contents and pits for recording disc information such as kind and recording capacity. The grooves are provided along the circumferential direction of the disc and its planar pattern wobbles with a predetermined width in the radial direction of the disc. The planar pattern of pits is oval shape and its overall shape is three-dimensional like a soccer-stadium shape. A plurality of pits are arranged along the circumferential direction of the disc thereby forming a track.
The grooves are formed in a data recording area and the pits are formed in a read-in track area so as to carry TOC (Table of Contents) information as the disc information as mentioned above or information such as pulse signals with predetermined cycle. In the conventional optical disc such as an MD, the area where the pits are formed and the area where the grooves are formed are mixed, and therefore form a spiral-shaped track as the whole disc.
In general, the width of the groove, which is used for recording data, is wider than that of the pit in order to record/read-out information precisely. In other words, when data is recorded on the grooves with a narrow width, noise increases and the S/N ratio decreases. Possibly, the data is recorded on land having the width wider than the groove. However, it is not practical since the phases of the neighboring grooves do not substantially coincide in the radial direction of the disc, so that the width of the land always varies, thereby making fluctuations of the reproducing signals significant. Therefore, it is preferable to record data on grooves having a wide width.
The recording/reproducing time of an MD of the related art is 60 minutes or 74 minutes. Recently, 80-minutes MD has also been proposed. In an ordinary MD, based on the unified standard and the like, a read-in track area where pits carrying TOC information and the like are formed is set to be the area a radius of 14.5 mm to 16.0 mm, and a data recording area where grooves for recording/reproducing data are formed is set to be the area a radius of 16.0 mm to 30.5 mm, respectively. The recording/reproducing time is determined depending on the recording/reproducing speed (linear velocity) of the grooves and the track pitch. In the MD standard, the linear velocity is from 1.20 m/s to 1.40 m/s both inclusive, and the track pitch is 1.60xc2x10.10 xcexcm.
The standards of MD comprising a sequential spiral-shaped track as described are shown in FIG. 1 in respect to recording/reproducing time, linear velocity at the time of reading data and the track pitch. Upon changing the recording/reproducing time from 60 minutes to 74 minutes, the linear velocity changes from 1.40 m/s to 1.20 m/s. Further, upon changing the recording/reproducing time from 74 minutes to 80 minutes, the linear velocity stays at 1.20 m/s as is the minimum value of the MD standard, whereas the track pitch is required to be changed from 1.60 xcexcm to 1.51 xcexcm. This is because it is necessary to reduce the linear velocity for reading or to further narrow the track pitch in order to increase the recording/reproducing time without changing the disc size or the optical pick-up characteristics of a data recording/reproducing apparatus.
In an optical disc such as an MD or a magneto-optical (MO) disc of the related art, the track of pits and the track of grooves are provided so as to form a spiral shape and the pitches of the pits and the grooves are the same. Therefore, in the conventional apparatus for fabricating a master used for manufacturing an optical disc, the concavo-convex patterns of the pits and the grooves are formed at a constant track pitch almost over the entire surface of the disc from the read-in track area where the pits are formed to the data recording area where the grooves are formed. Accordingly, changing of the track pitch is not taken into consideration but various kinds of techniques have been developed to maintain a constant track pitch as precise as possible.
Especially, in case of MD capable of recording/reproducing for 80 minutes, it is necessary to narrow the track pitch of the grooves between 1.50 xcexcm and 1.51 xcexcm, which is narrower than 1.60 xcexcm in the related art. Therefore, the track pitches of the pits and grooves are standardized to 1.50 xcexcm.
However, there may be a case where optical detection of the pits becomes difficult or impossible when both of the track pitches of the pits and grooves are set to be as narrow as 1.50 xcexcm. In the MD standard, servo signals such as push-pull signal and RC (Radial Constant) and the signal characteristic of the pits are determined and standardized based on the track pitch of 1.60 xcexcm. Therefore, if the track pitch is 1.50 xcexcm, it is difficult to meet the standard of general recording/reproducing characteristic established in the MD standard in terms of push-pull signal, crosstalk and the like especially regarding the pits.
The invention has been designed to overcome the foregoing problems. The object of the invention is to provide: a recording medium capable of complying with the standard of recording/reproducing characteristic established in the MD standard and capable of reliably performing optical detection of the pits in an optical disc or a magneto-optical disc in which the pit string and the pattern of the grooves in the longitudinal direction are provided to form a sequential spiral-shaped track; a master used for fabricating the recording medium; and a method of manufacturing the recording medium and the recording medium master.
A recording medium of the invention comprises pits and grooves on a surface of a disc-shaped substrate being arranged so as to form a spiral-shaped track, and is formed to be capable of reading information carried in the pits and the grooves by irradiating a laser with a wavelength of 0.78xc2x10.01 xcexcm and NA of 0.45xc2x110.01 along the track. The ratio of track pitch of the pits to the track pitch of the grooves is from 1.00 exclusive to 1.13 inclusive.
A recording medium of the invention comprises pits and grooves on a surface of a disc-shaped substrate being arranged so as to form a spiral-shaped track, and is formed to be capable of reading information carried in the pits and the grooves along the track. The ratio of track pitch of the pits to the track pitch of the grooves is from 1.00 exclusive to 1.13 inclusive.
In a recording medium and a recording medium master, and a method of manufacturing a recording medium of the invention, the track pitch of the pits is wider than that of the grooves and the ratio is from 1.00 exclusive to 1.13 inclusive. In the related art, the track pitches of the pits and grooves are the same. This may result in difficulty or impossibility of the optical detection of the pits. In the present invention, the track pitch of the pits is wider than that of the grooves and its ratio is from 1.00 exclusive to 1.13 inclusive. This enables to perform reliable optical detection of the pits.
By setting the track pitch of the grooves from 1.50 xcexcm inclusive to 1.70 xcexcm exclusive, recording/reproducing of various kinds of information on/from a recording medium of the invention can also be performed using an ordinary data recording/reproducing apparatus with the track pitch of 1.60xc2x10.10 xcexcm.
For example, in order to achieve a recording medium capable of performing a high-capacity or a long-time recording/reproducing such as an MD which is capable of recording/reproducing for 80 minutes, it is necessary to increase the data storage capacity by setting the track pitch of the grooves as narrow as about 1.51 xcexcm. In this case, if the track pitch of the pits is 1.13 times of the track pitch of the grooves, which is the maximum ratio as mentioned above, the track pitch of the pits is about 1.70 xcexcm. Thereby, the track pitches of both the grooves and pits are within the permissible range of 1.60xc2x10.10 xcexcm, which is a requirement of the track pitch in a standard data recording/reproducing apparatus. Therefore, the track pitches of both the pits and grooves can read/write information with a standard data recording/reproducing apparatus.
The present invention is preferable specifically for a recording medium which complies with the standards of MD 80 and the master, and a method of manufacturing the recording medium. However, it is not limited to these.
Other and further objects, features and advantages of the invention will appear more fully from the following description.